Following are acronyms used in the description below:
MMR mobile multihop relay
BS base station
RS relay station
SS subscriber station
MS mobile station (one type of SS)
DL downlink
UL uplink
OFDMA orthogonal frequency division multiplexing access
TTD time division duplex
IEEE 802.16j standardization task group is working on MMR (Mobile Multihop Relay) enabled networking in WiMAX systems. FIG. 1 illustrates a network 10 environment with various usage scenarios being addressed by that 802.16j Task Group. A BS 12 provides coverage to various SSs within a cell 14, which may or may not be regularly shaped. MMR is one technique to address coverage gaps within the cell 14, and also to extend coverage beyond the edges of the cell 14. RSs 16 are used to relay signals from the BS 12 to the SSs, and where appropriate from the SSs back to the BS 12. For example, an RS 16 may be used to provide more robust coverage within a building 18; within a tunnel 20, in a valley between buildings 22a or shadow of a building 22c or other coverage hole 22b within the cell 14; an RS 16 may be used to extend coverage of the BS 12 beyond an edge of the cell as shown at the cell extensions 26a and 26b-26c. Two usage scenarios are of note. The multihop aspect of MMR is shown in the cell extensions 26b and 26c, which extend coverage by the BS 12 by a series of two or more RSs 16. While some RSs 16 may be stationary as in the depicted towers, some may also be mobile as with the RS 16′ disposed on the subway car (perhaps multi-hopping through other RSs 16 fixed within the tunnel 20) and the RS 16′ disposed on the bus so as to enable robust coverage for riders. SSs are the end users that do not form part of the network 10 but rather access its services, typically on a subscription or prepaid basis. MSs 22 are the most common type of SS, though SSs need not be mobile in general. MMR therefore extends cell 14 coverage, and enhances link budget for indoor 18 or underground 20 penetration where the direct signal to and from the BS 12 would be otherwise insufficient.
Usage models are also used to describe the different reasons that a network operator/carrier may deploy RSs. The key reasons that a carrier might deploy RSs are:                Enhanced Data Rate Coverage—Provide higher uniform signal to interference noise ratio SINR to users within the cell 14. This can also be thought of as providing higher throughput to individual MSs 22 within the entire cell.        Range Extension—Provide coverage to users outside the edge of the cell.        Capacity Enhancement—increase system capacity by deploying RSs in a pico-cell deployment enabling more aggressive frequency reuse.        
MMR in a network may provide range extension of cellular coverage and improve the system data throughput. On the other hand, a MMR-enabled networking scheme may also increase the system complexity that includes the hardware entity cost of the relay station, the signaling overhead between BS-RS-MS/SS (Mobile Station/Subscriber Station), and the interference between two overlapped RS coverages. Interference arises because the BS has limited resources from which to assign to the various RSs. Where more than one RS is in operation within a single cell 14, they may be proximal enough that channels interfere. With the increased density of RS in overlapping coverage areas, and due to the mobility of some RSs, the probability of co-channel interference between BS and RS as well as between adjacent RSs increases. Further, the BS is allocated by the network only certain frequencies/spreading codes for effecting communications within its cell 14, and these must also be managed among the RSs in order to accommodate the maximum number of SSs without sacrificing quality.
Since MMR is only recently proposed in IEEE 802.16j, channel assignment and frequency reuse in the RS level is a new problem. To the best of the inventors' knowledge, no previous solution has been presented to address co-channel interference and resource allocation among RSs of a MMR system.